According to the Center for Disease Control and Prevention (CDC), a concussion is, "a type of traumatic brain injury-or TBI-caused by a bump, blow, or jolt to the head or by a hit to the body that causes the head and brain to move rapidly back and forth. Even a mild blow or "getting your bell rung," can be a serious matter. Signs of a concussion may not show up until days or weeks after the injury. 

This sudden movement can cause the brain to bounce around or twist in the skull, creating chemical changes in the brain and sometimes stretching and damaging brain cells. Seek medical attention right away if you notice any signs of concussion in your child.